Microwave ovens are widely used all over the world to heat and cook food items much more rapidly than conventional heating ovens. But the nature of microwave technology is such that in the process of heating food items, the microwaves will often cause the food items to overflow, or to "pop," which of course, produces a mess along the sides, back and front (interior surface) of the microwave oven that needs to be cleaned with a sponge or similar cleaning apparatus. This entails reaching into the oven and applying "elbow grease" at various awkward angles, and as anyone who uses and has ever had to clean a microwave oven is aware, is tiresome and difficult.
The U.S. Patent literature does disclose some efforts to solve this problem. U.S. Pat. Nos. 4,721,140; 4,785,160; 4,797,523; 4,801,773; and 4,950,859, for example, all disclose various containers, covers, shields, etc., that are placed over or around a particular food item being cooked, in order to block and prevent spills and spatters from that food item from reaching the inner surface of the microwave oven. But these are associated in their use with each individual food item being cooked, rather than with the microwave oven itself. As such, these devices are removed along with the associated food item each time a food item is heated or cooked, and reintroduced into the microwave oven each time a new food is to be cooked.
U.S. Pat. Nos. 4,663,052; 4,778,968; and 5,290,985 improve this situation, since these protective devices are each used in connection with the microwave oven itself, and remain in place to guard against spills and spatter from the cooking of one food item to the cooking of subsequent foods items. After a time, once the protective device has become soiled beyond a certain point, the device is removed and disposed of, and is replaced with a new, similar device.
But microwave ovens are manufactured and sold in many varied sizes, and all of U.S. Pat. Nos. 4,663,052; 4,778,968; and 5,290,985 suffer the common deficiency that they cannot easily be used in connection with varying sizes of microwave oven. Indeed, a survey taken by applicants of over 100 microwave oven models reveals that microwave ovens typically vary in volume from about 0.5 to 1.8 cubic feet, and in linear dimension from a minimum height of about 6 inches to a maximum height of about 15 inches, from a minimum width of about 11 inches to a maximum width of about 21 inches, and from a minimum depth of about 10 inches to a maximum depth of about 18 inches. This survey also reveals that these linear dimensions typically vary by 1/4 inch, 1/8 inch, 1/6 inch, or 1/16 inch increments. Given this wide size variability from one microwave oven to the next, it would be difficult or impossible to use the protective devices of U.S. Pat. Nos. 4,663,052; 4,778,968; and 5,290,985 for more than a single size of microwave oven, give or take perhaps a fraction of an inch along any one linear dimension. As such, if these protective devices were to be used for all commonly-manufactured oven sizes, it would be necessary to manufacture dozens of different sizes of these protective devices.
In addition, all of these liners are difficult to set up and attach for use inside the microwave oven, and (e.g., U.S. Pat. No. 4,778,968, column 2, lines 58-61) even need an independent support structure.
These liners also do not appear to provide suitable protection for the front door of a microwave oven.
Additionally, the choice of materials used to construct a microwave liner is very important. Saran-type polymeric materials do not hold up well over time and are meant for one use and then disposed of. They do not have a heat history at all, melting in the presence of steam resulting from cooking food. Cardboard-type material and papers commonly used in paper bag construction are not appropriate either. These materials absorb moisture and spilled foods. This causes them to stick to the microwave interior, defeating their purpose and usefulness.